The disclosed invention generally relates to mini chip carrier arrays, and is particularly directed to a mini chip carrier array wherein individual chip carriers are separated by elongated slots each of which accommodate a plurality of wrap-around edge interconnects for each adjacent chip carrier.
Integrated circuit chips utilized in complex hybrid circuits are often mounted on individual ceramic carriers. Typically, the ceramic carrier is bonded to the hybrid circuit motherboard by soldering the edge interconnects of the ceramic carrier to corresponding conductors on the motherboard.
Ceramic carriers are typically fabricated in unitary arrays wherein each chip carrier array includes a matrix of interconnected chip carriers. Each chip carrier includes a plurality of metallized wrap-around edge interconnects which pass through holes or slits formed along the boundaries between the individual chip carriers and along the chip carrier edges adjacent the substrate waste edge. In some arrays, each hole or slit between adjacent chip carriers accommodates two wrap-around edge interconnects, one from each adjacent chip carrier, while each hole or slit adjacent the substrate waste edge accommodates a single wrap-around edge interconnect for the adjacent chip carrier. In other arrays, a separate hole or slit is provided for each wrap around interconnect.
Typically, the wrap-around edge interconnects are applied by silk screen printing and vacuum pull-through techniques. For arrays having holes or slits between adjacent carriers for accommodating two edge interconnects, the edge interconnects are applied by shared metallization. However, in order to maintain electrical isolation between edge interconnects sharing the same hole or slit, the size of the hole or slit has to be sufficiently large to avoid a short circuit in the metallization process. Thus, the minimum spacing between edge interconnects of an individual chip carrier is limited by a minimum hole or slit size and the necessary spacing between adjacent holes or slits. Such limitation in turn limits the minimum chip carrier size.
The electrical isolation referred to above allows for electrical testing of the entire chip carrier array prior to separation of the array into individual chip carriers. Of course, if such testing is not necessary, then smaller holes or slits could be tolerated to achieve closer spacing of the edge interconnects. However, separation of the array into individual chip carriers could cause damage to the chip carriers having short circuited edge interconnects.
The arrays wherein each edge interconnect has its own hole or slit allows for closer spacing, but the minimum spacing is still limited since metallization within a hole or slit becomes more difficult as its size decreases. Moreover, the production of such a chip carrier array is more complex and expensive.
A further disadvantage of known chip carrier arrays is that corners of individual chip carriers randomly break when the array is separated into individual chip carriers. Such breaking typically damages edge interconnects, thereby rendering useless each chip carrier having a damaged conductor. To the extent that integrated circuit chips are mounted on the chip carriers prior to separation of the chip carrier array, a damaged chip carrier also results in a wasted integrated circuit.
Another disadvantage of known chip carrier arrays is the high cost of production resulting from (1) the necessary laser fabrication of numerous through holes or slits, (2) the difficulty of inspecting individual chip carriers, and/or (3) the reduced yield caused by breakage.